1. Field of the Invention
The invention relates to a waveform compression and expansion apparatus with which a waveform is compressed or expanded in the direction of the temporal axis.
2. Description of Related Art
For some time, the changing of the pitch of musical tones etc. by transforming the pitch of the signal that expresses the waveform of the musical tones etc., the so-called pitch shifter, has been known. However, when the pitch of a signal that expresses the waveform of a phrase, which has a length to the degree that the tempo of the musical tones is known, is transformed by the pitch shifter, there is a problem in that the tempo of the musical tones is also changed and there has been a desire for a system with which only the pitch is changed without changing the tempo of the musical tones. Conversely, a system with which the tempo is changed while the pitch of the musical tones is preserved has also been desired.
As a system that responds to these demands, a waveform compression and expansion apparatus with which the waveform of the musical tones etc. is compressed or expanded in the direction of the temporal axis independently of the alteration of the pitch has been proposed.
However, a multiple number of compression and expansion formats can be considered as the format with which the waveform will be compressed or expanded. In addition, with regard to the waveform that expresses the sound, there are various kinds of waveforms such as periodic waveforms, aperiodic waveforms, intermittent waveforms and continuous waveforms and, a compression and expansion processing format can be considered that appropriately compresses or expands the waveform in the direction of the temporal axis in conformance with the type of waveform. That is to say, for a given waveform, when the compression and expansion are carried out with a format that is appropriate to the variety of that waveform, the tonal quality of the sound that is expressed by the waveform following compression and expansion will be satisfactory. However, in the case where, for a given waveform, the compression and expansion is done with a format that is not appropriate to the variety of that waveform, the tonal quality of the sound that is expressed by the waveform following compression and expansion will be poor.
However, in general, the waveforms of musical tones etc. are waveforms in which various kinds of waveforms have been mixed together. Because of this, no matter which compression and expansion processing format is employed, there is a problem in that it is likely that the tonal quality of the musical tones etc. that is expressed by the waveform following the compression and expansion of the waveform of the musical tones etc. will be poor.